Stoker control system, including delayed air feed



Oct. 4, 194-9. SAGAR 2,483,847

STOKER CONTROL SYSTEM, INCLUDING DELAYED AIR FEED Filed May 22, 1945 Z'mnentor:

Gtfomeg Patented Oct. 4, 1349 STOKER CONTROL SYSTEM, INCLUDING DELAYED AIR FEED Paul B. Sagar, Cleveland, Ohio, assignor to General Controls 00., Glendale, Calif., a corporation of California Application May 22, 1945, Serial No. 595,235

2 Claims.

This invention relates to improvements in stoker control systems for coal furnaces.

A coal stoker of the type commonly in use comprises mechanical means for feeding coal to the furnace and a fan for supplying the air necessary for combustion of the coal; an electric motor serving to operate both the coal-feeding means and the fan when the motor is energized under the control of means, such as a room thermostat, in response to demand for acceleration of combustion in the furnace. In order to prevent the possibility of the fire burning to a low level in the furnace when demand for heat is infrequent, an additional, or refueling, control means is usually provided whereby the motor is energized during predetermined periods regardless of the condition of the room thermostat. By supplying the full amount of air to the furnace along with the coal during the refueling operation, a consider able amount of the coal is consumed directly as it is introduced and most of the heat thereby generated is normally wasted. It is therefore an object of this invention to minimize burning of fuel during the refueling operation so as to reduce heat-release, decrease the amount of coal for hold-fire requirements, and to prevent burning of the fire to too low a level during idle periods; this object being accomplished by the provision of means whereby during the refueling periods the supply of combustion air is reduced or entirely excluded.

In connection with the operation of a stoker control system of the character described in the preceding paragraph in response to normal heating demands, it is a further object of this invention to provide means for delaying full supply of air to the furnace for a predetermined period following initiation of feeding of the coal so as to compensate for the coal consumed during idle periods and thereby maintain a relatively uniform level of the fire.

Other objects and advantages of the invention will be found in the description, the drawing, and the claims; and, for full understanding of the invention, reference is to be had to the following detailed description and accompanying drawing, the single figure of which is a diagrammatic view of a stoker control system embodying the invention.

In the drawing, the numeral ll indicates a furnace into which coal from a hopper I2 can be fed through a conduit l3 which contains suitable conveying apparatus (not shown) operated by an electric motor I4. Operated concurrently by this motor is a fan or blower l5 which is adapted to force air through a duct I6 for combustion of the coal in the furnace. Indicated at I! is a pair of electric service lines, one of which is connected directly to one terminal of motor I4 and the other to the fixed contact [8 of an electromagnetic relay l9. When current is passed through the coil 26 of the relay, the contact arm 2| is attracted from its normally-open position, as shown, into engagement with the fixed contact [8 to complete the motor-energizing circuit through a wire 22, connected to the other motor terminal, and a safety device 23 which, for example, may be a limit control adapted to open the motor circuit upon abnormal rise of temperature in the furnace.

Connected by wires 24 to the service lines I! (which, it is to be assumed, supply alternating current) is the primary 25 of a step-down transformer 26. One terminal of the secondary 21 of the transformer is connected directly to one lead of relay-coil 20, the other terminal of the secondary being connected by wires 28 and 29 to the fixed contact 30 of a thermostat 3! which, it is to be assumed, is arranged to respond to the temperature of a space or room heated by the furnace H. The bimetallic contact member 32 of the thermostat is connected by a wire 33, in series with a resistor or heating element 34, to a contact element 35 with which a pivoted contact arm 36 cooperates. This arm is operated by rotation of a disk 31 which is driven at a constant speed by a small electric motor 38 which, it is to be assumed, is continuously energized while the control system is in operation; the disk 31 having a raised or cam portion 39 which is adapted in the rotation of the disk to move the arm 36 out of engagement with the contact element 35 and into engagement with another contact element 40 which is connected to the wire 28. The arm 36 is connected by a wire 4| to the other lead of relay-coil 20.

Within the air-duct I6 is a damper 42, to an outer end of the mounting rod 43 of which is attached an arm 44. The damper is biased by gravity to duct-closing position, as shown, and is adapted to rotate in a clockwise direction toward open position under the pressure of the air supplied to the duct by fan I5. Rotation of the damper toward open position is normally limited to a small angle by means disposed in the path of movement of damper-arm 44. This means comprises the hooked extremity 45 of a member 46, which member is pivoted at 41 and connected intermediate its ends to the plunger 48 of an electromagnetic solenoid 49.

When the solenoid is energized by passage of current through its coil 50, the resultant attraction of the plunger raises the member 46 so that the damper is then freed for movement to fully-open position. The solenoid-coil 50 is connected across the secondary 21 of transformer 25 by Wires 5! and 52, a thermostatic circuit-controlling device 53 being inserted in series in the wire 52. The device :53 comprises a fixed contact element 54 and a bimetallic contact blade 55, the blade being so arranged that under the influence of heat it warps toward engagement with contact element 54 to complete the energizing circuit of solenoid 49. Associated with the device 53, so as to constitute the same a thermal time-delay, is the heating element 34.

With the parts in the positions shown in the drawing the stoker system is idle. When demand for acceleration of combustion in the furnace is evidenced by closing of the contacts of roomthermostat 3|, the energizing circuit of relay is is complete; the circuit being traced from the upper low-voltage terminal of transformer 25 through wires 2829, fixed contact 33, contact member 32, wire 33, heating element St, wire 33, contact element 35, contact arm 38, wire 5!, and relay-coil 20 to the other low-voltage terminal. It will be understood that the resistance of heating-element 34 is low with respect to that of the relay coil and hence does not materially impede the flow of current. The resultant attraction of relay contact-arm 2i efiects energization of the motor I4 and operation of the stoking apparatus and fan 15. However, since the solenoid 39 is at present unenergized and opening movement of damper 42 therefore limited to a small angle, only a small amount of air can pass to the furnace for combustion of the coal now being introduced. The heat produced by the current flowing through the resistor 34 effects warpage of blade 55 so that after a predetermined period the energizing circuit of solenoid s9 is completed and the damper 42 is freed for movement to fully-open position under the air pressure produced in the duct by fan iii. The construction and arrangement. of the elements of the time-delay device determine the delay period, which under average conditions may be of the order of one minute. As was mentioned hereinabove in the statement of invention, the coal initially introduced compensates for that consumed during the idle period so that the fire is maintained at a more uniform level. Under some operating conditions it may be preferable to so arrange the damper latch that no appreciable amount of air can pass through the duct to the furnace until the damper is released. In place of the latched damper arrangement, shown by way of illustration, other convenient means for controlling air passage through the duct can be employed; the feature of the invention in its broadest aspect being to delay the entrance of any substantial amount of combustion air for a definite period after feeding of the coal is begun.

In order to hold-fire in the furnace, the stoker is periodically operated under the control of the time-responsive means comprising elements 35-40. When, by rotation of disk 35, the contact arm 36 is moved from its position as shown into engagement with contact element 40, the relay I9 is then energized; the circuit being from the top low-voltage terminal of the transformer 26 through wire 28, contact element 40, contact arm 36, wire 3|, and relay coil 20 to the bottom low-voltage terminal. Concurrent operation of the stoking apparatus and fan I5 is therefore efiected, but since the damper is latched in minimum-flow position by engagement of damper-arm 44 with member 46, only a small proportion of the air supplied by the fan passes to the furnace. The circuit which includes heating element 34 having been interrupted by the movement of contact arm 36, energization of solenoid 49 to release the damper is precluded while the cam portion of disk 31 is in engagement with the contact arm 36, so that substan tially only the coal is supplied to the furnace during that period and no wasteful combustion takes place. The disk 31 is conveniently arranged to rotate at a speed of one revolution per hour, and the length of the cam surface 39 may be such that the refueling period is of the order of three minutes under average conditions.

The embodiment of my invention herein shown and described is obviously susceptible of modification without departing from the spirit of the invention, and I intend therefore to be limited only by the scope of the appended claims.

I claim as my invention:

1. In an electrical stoker-control system: a coal furnace; mechanical means for feeding coal to the furnace; means forming a duct for supplying combustion air to the furnace; a fan for forcing air into said duct; an electric motor for concurrently operating said coal-feeding means and said fan; means in said duct normally restricting flow of air therethrough; electrical means for rendering said flow-restricting means ineffective so that full amount of air can pass through the duct; a first electrical circuit-portion including a thermostat, responsive to the demand of a space heated by the furnace, and also including means electrically energizable to effect delayed operation of said electrical means; a second electrical circuit portion including a source of electrical energy and means for effecting operation of said motor; switching means effective in one position to interconnect said circuit-portions so that oper ation of said motor and of said delayed-operating means is then under the control of said thermostat, said switching means having another position wherein said circuit-portions are uninterconnected and said second circuit-portion is closed so that operation of the motor is then effected independently of the control of said thermostat; and time-controlled means for periodically operating said switching means from said one position to said other.

2. In an electrical Stoker-control system: a coal furnace; mechanical means for feeding coal to the furnace; means forming a duct for supplying combustion air to the furnace; a fan for forcing air into said duct; an electric motor for concurrently operating said coal-feeding means and said fan; means in said duct normally restricting flow of air therethrough; means for rendering said flow-restricting means ineffective so that full amount of air can pass through the duct; a slowoperating heat-motor for operating said lastnamed means; a first electrical circuit-portion including a thermostat, responsive to the demand of a space heated by the furnace, and also including an electric heater for operating said heat-motor; a second electrical circuit-portion including a source of electrical energy and means for effecting operation of said electric motor; switching means effective in one position to interconnect said circuit-portions so that operation of said electric motor and of said electric heater is then under the control of said thermostat, said switch- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Jones May 23, 1911 Crouch Mar. 18, 1913 Stuart June 28, 1938 Birkenbeuel July 12, 1938 Selig, Jr Oct. 22, 1940 Tate Dec. 9, 1941 Selig, Jr Feb. 3, 1942 Hotchkiss Oct. 17, 1944 Stuart Apr. 3, 1945 Miller June 5, 1945 

